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United States Patent |
6,068,684
|
Overton
|
May 30, 2000
|
Microstructure chromatograph with rectangular column
Abstract
A novel chromatograph is provided. The chromatograph includes an analytical
column which is a channel with a rectangular cross-section. Integrated
with the chromatograph are a sample collection channel and a restriction
channel. The column, sample collection channel, and restriction are all
part of a single unitary microstructure. The microstructure is
manufactured by irradiating and etching a material subject to synchronized
x-ray radiation. The device will either be made of the actual etched
material, or the etched material will be used as a mold or model to
fabricate the chromatograph. A method of using the device is also
disclosed.
Inventors:
|
Overton; Edward B. (Baton Rouge, LA)
|
Assignee:
|
Board of Supervisors of Louisiana State University and Agricultural & (Baton Rouge, LA)
|
Appl. No.:
|
927168 |
Filed:
|
September 11, 1997 |
Current U.S. Class: |
96/104; 96/105; 96/107; 210/198.2; 210/656 |
Intern'l Class: |
B01D 015/08 |
Field of Search: |
210/656,659,198.2
96/101,104,105,107
|
References Cited
U.S. Patent Documents
3097518 | Jul., 1963 | Taylor et al. | 73/23.
|
3150517 | Sep., 1964 | Kuffer et al. | 73/23.
|
3174326 | Mar., 1965 | Carle et al. | 73/23.
|
3503712 | Mar., 1970 | Sussman | 23/252.
|
3662520 | May., 1972 | Saunders | 55/158.
|
3668834 | Jun., 1972 | Deans | 55/67.
|
3748833 | Jul., 1973 | Karas et al. | 55/197.
|
4604198 | Aug., 1986 | Dailey | 210/198.
|
4908112 | Mar., 1990 | Pace | 210/198.
|
4935040 | Jun., 1990 | Goedert | 15/8.
|
5116495 | May., 1992 | Prohaska | 210/198.
|
5165292 | Nov., 1992 | Prohaska | 210/198.
|
5376252 | Dec., 1994 | Ekstrom | 210/198.
|
5378583 | Jan., 1995 | Guckel et al. | 430/325.
|
5500071 | Mar., 1996 | Kaltenbach | 210/198.
|
5544276 | Aug., 1996 | Loux | 96/102.
|
5549819 | Aug., 1996 | Nickelson | 210/198.
|
5571410 | Nov., 1996 | Swedberg | 210/198.
|
5580523 | Dec., 1996 | Bard | 210/198.
|
5611846 | Mar., 1997 | Overton et al. | 96/102.
|
5641400 | Jun., 1997 | Kaltenbach | 210/198.
|
5646048 | Jul., 1997 | Templin | 210/198.
|
5658413 | Aug., 1997 | Kaltenbach | 210/198.
|
5792943 | Aug., 1998 | Craig | 210/198.
|
Other References
Preparative Capillary Chromatography--A Proposal, pp. 6-7, Journal of High
Resolution Chromatography & Chromatography Communications, Jan. 1988.
The Height Equivalent To A Theoretical Plate of Retentionless Rectangular
Tubes, pp. 1-8, Journal of Chromatography, 1981.
|
Primary Examiner: Therkorn; Ernest G.
Attorney, Agent or Firm: Kean, Miller, Hawthorne, D'Armond, McCowan & Jarman, Primeaux; Russel O.
Claims
I claim:
1. A GC sensor comprising an analytical column with an intake end and a
detector end, said column having a substantially rectangular cross-section
and said column being formed by a series of parallel passages connected at
alternating ends in a substantially planar microstructure.
2. The GC sensor in claim 1 wherein said height of said cross-section is
equal to or greater than approximately three times said width.
3. The GC sensor in claim 1 wherein:
(a) said column further comprises an inner surface;
(b) a liquid phase is disposed along said inner surface; and
(c) the column width and height are selected such that as analytes are
moved through said column molecules of said analyte will elute and exhibit
relatively no movement in the direction parallel to a line along which
said height is measured, but said molecules will exhibit substantially
laminar flow as said molecules travel toward said detector end.
4. The device in claim 3 further comprising:
(a) a sample section having a sample section carrier inlet and a sample
inlet;
(b) a restrictor fluidly connected between said sample section and said
intake end of said column;
(c) said sample section, said restrictor, and said column being part of a
continuous channel contained in a channel structure having a bottom layer;
and
(d) a top plate bonded to said channel structure.
5. The device in claim 4 further comprising a temperature control means
bonded to said bottom layer or said top plate of said channel structure.
6. The device in claim 5 wherein said temperature control means is a
Peltier cooler or a resistance heater.
7. The device in claim 5 wherein said top plate further comprises a
manifold.
8. The device in claim 7 wherein said temperature control means is a
Peltier cooler or a resistance heater.
9. A device for chromatography comprising:
(a) two or more GC sensors, each said sensor comprising:
(i) an analytical column with an intake end, a detector end, an inner
surface, and a liquid phase disposed along said inner surface, said column
having a substantially rectangular cross-section;
(ii) the column width and height for said rectangular cross-section being
selected such that as analytes are moved through said column molecules of
said analyte will elute and exhibit relatively no movement in the
direction parallel to a line along which said height is measured, but said
molecules will exhibit substantially laminar flow as said molecules travel
toward said detector end;
(iii) a sample section having a sample section carrier inlet and a sample
inlet;
(iv) a restrictor fluidly connected between said sample section and said
intake end of said column;
(v) said sample section, said restrictor, and said column being part of a
continuous channel contained in a substantially planar channel structure
having a bottom layer; and
(vi) a top plate bonded to said channel structure;
(b) an array housing to which said GC sensors are interchangeably attached;
and
(c) each said sensor being adapted to detect one or more specific compounds
which the other sensors in said array housing are not adapted to detect.
10. A GC sensor comprising an analytical column with an intake end and a
detector end, said column having a substantially rectangular
cross-section, and said column being formed by a series of parallel
passages connected at alternating ends in a substantially planar
microstructure, said GC sensor being produced by the following method:
a. providing a substrate of material susceptible to x-rays and etching;
b. irradiating selected portions of said substrate material with
synchronized x-ray radiation, said selected portions being chosen such
that after etching a microstructure with three sides of said rectangular
cross-section columns will be formed, the long sides of said rectangular
cross-section being parallel to the path of said radiation;
c. etching the material in an etching solution; and
d. bonding a top to said material to form the fourth side of said
rectangular cross-section of said column.
11. A GC sensor comprising an analytical column with an intake end and a
detector end, said column having a substantially rectangular
cross-section, said GC sensor being produced by the following method:
a. providing a layer of metal bonded to a substrate of material susceptible
to x-rays and etching;
b. irradiating selected portions of said material with synchronized x-ray
radiation, said selected portions being chosen such that after etching a
microstructure with three sides of said rectangular cross-section columns
will be formed, the long sides of said rectangular cross-section being
parallel to the path of said radiation;
c. etching the material in an etching solution;
d. electroplating metal onto the metal plate so as to fill the portions
which were etched away;
d. filling the resulting metal structure with quartz such that a quartz
microstructure with three sides of said rectangular cross-section column
will be formed; and
e. bonding a top to said quartz microstructure to form the fourth side of
said rectangular cross-section of said column.
12. A GC sensor produced by the method in claim 11, comprising the
additional step of coating the interior surfaces of said column with metal
.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates, generally, to analyses using devices for liquid and
gas chromatography, and particularly to very small chromatographic devices
and analyses.
2. Prior Art
Chromatography is the group of separation techniques in which a mobile
phase (either a gas or liquid) is flowed over a stationary phase (either
liquid or solid). As the mobile phase moves past the stationary phase,
repeated adsorption and desorption, or partitioning, of the solute occurs
at the rate determined chiefly by the solute's ratio of distribution
between the two phases (partition ratio, K).
A gas chromatograph (GC) is an analytical instrument which uses the
principle discussed above to separate and identify the solute compounds as
a gas that are present in a sample. Typical GCs will include an analytical
column with a gas carrier source and sample inlet at one end and a
detector at the other end. The device which obtains the sample, and which
extracts the analytes from the sample, can either be integrated with the
GC or be a separate device.
Most GC's will include a means of heating the column as the analytes are
moved through the analytical column by the carrier gas. In conventional
GC's the heating is achieved by enclosing the entire column within an
oven, and the oven GC's are very bulky devices. Some advances have been
made in the field to allow for smaller gas chromatographs. For example,
newer means for heating the column have been discovered. U.S. Pat. No.
5,611,846 to Overton et al discloses a GC which uses electrically
resistive heater wire placed adjacent to the analytical column for heating
of the column. This configuration allows for a device of less bulk than
conventional oven GCs. However, even the device of the '846 patent is not
built to such a miniature scale so as to be easily adaptable to personal
sensor applications.
The need is clear and urgent for speciating chemical sensors that respond
to the concentration of specific chemicals in complex mixtures.
Conventional GCs and gas chromatograph/mass spectrometers (GCMS) have the
capability to respond to the concentration of specific substances in
complex mixtures but are certainly not "sensors" in terms of their size
and functionality. If the speciating capability of certain conventional GC
instruments could be fitted into the small size and operational
functionality of common sensors, this development would result in a true
speciated chemical sensor.
In this application, the name "GC sensor" will be used to describe this new
type of analytical instrument that uses gas chromatographic technology for
its speciating analytical capability. If GCs could be sufficiently
miniaturized to function as GC sensors, multiple GC sensor modules could
be placed in an array within a single instrument. Each GC sensor in this
array could be designed for the performance of separate analytical
functions. Redundant and simultaneous testing could be done, or each GC
sensor could be designed to test for a specific compound. Currently, such
selectivity is only achievable with large and expensive "hyphenated"
analytical instruments such as GCMS.
Selectivity is extremely vital in GC in applications such as bomb and
chemical warfare agent detection. Multiple GC sensor modules can also be
tailored to provide analyses of compounds with widely different chemical
characteristics. For example, one sensor module could be fitted with a
molecular sieve column for separation of the permanent gases such as
hydrogen, nitrogen and oxygen while another sensor module could be fitted
with a column for the separation of BTEX components, or hydrocarbons in
the range C14 to C25.
In many GC applications one desires to perform testing which requires two
or more GCs. If one wants to test across an extremely broad dynamic range
one must use multiple instruments, with their attendant bulk. Miniature GC
devices would allow such testing to be done in a field environment.
Miniaturization also decrease the power requirements of conventional GCs.
Conventional GCs are currently designed to handle a very wide variety of
analytical applications. The disadvantage of this design philosophy is
that each instrument has much unused capability in any given application.
Unused capability in analytical instruments translates into extra cost,
size, power consumption, and complexity. There is a need for small,
rugged, and relative inexpensive analyzers that have satisfactory
performance within certain applications but, in general, cannot be applied
to a wide variety of other applications. Analytical instruments using GC
sensor modules need not have all the analytical capability of laboratory
devices, but if needed the instruments could be designed with such
capability.
Outside of the field of gas chromatography, many advances have been made in
the miniaturization of mechanical as well as electrical devices. One
technique for the manufacture of very small devices is the use of
synchronous x-ray radiation, such as that available from a synchrotron, to
irradiate material which is sensitive to the radiation. The material can
then be etched, leaving very fine and intricate structures.
The remaining structure can itself be the actual desired structure, or it
can be used as a mold for the electrodeposition of metal. Again, the
deposited metal structure can be the desired structure, or it too can
serve as a mold for other materials. The resulting device, whether created
from a mold or directly from the etching process, is extremely small and
has extremely high resolution. It also can have extremely tall, accurate,
and sharp vertical structures, and for this characteristic the devices are
referred to herein as high aspect ratio microstructures (HARMs). HARMs
have been made in various configurations such as valves, switches and heat
exchanger surfaces. However, the inventor is unaware of any adaptation of
HARMs to gas chromatography.
Many applications of GC analysis, spanning a wide variety of fields,
require decisions to be made based on the concentration of specific
chemical compounds in complex mixtures. This type of analysis, analysis
that provides data on concentrations of specific chemical species, is
called compound-specific analysis. Compound specific analysis can be used
in environmental, medical, industrial, transportation, energy,
service/facilities, educational, military, and other applications.
Specific examples of applications for a device which incorporates one or
more GC sensors capable of compound-specific analysis could include:
an airport security guard using the device to check for explosives;
police using the device to search a cruise ship following a bomb treat;
using the device to monitor a subway station for chemical nerve agents
following reports of a strange odor in the station;
emergency officials using several devices located throughout a city to
detect chemical emissions during a fire at a nearby chemical manufacturing
plant, and order evacuations as appropriate;
a customs inspector using the device to detect contamination of foodstuffs
by an illegal pesticide;
a petrochemical plant increasing its efficiency and product quality by
monitoring process streams with many devices to rapidly detect unwanted
deviations from operational and product specifications;
a medical professional using the device to perform rapid, inexpensive,
non-invasive screening for metabolic diseases; and
a commodity inspector using the device to detect the freshness of raw
product.
Current "sniffing" technology is not technology at all, but instead relies
on dogs in serious situations involving drugs and explosives. There are
myriad other applications which will arise given our technology driven
society.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a GC analytical device
which is small enough for use as a hand-held device.
Another object of the present invention is to provide a GC-based analytical
device which is smaller and lighter than current GCs.
Another object of the present invention is to provide a CG sensor which is
adaptable for multiple GC sensors in arrayed configurations.
Another object of the present invention is to provide a sensor type device
which is capable of compound-specific analysis.
Another object of the present invention is to provide a GC device which can
be manufactured using HARM manufacturing techniques.
Another object of the present invention is to provide a GC sensor which is
adaptable to temperature programming techniques and which has the ability
to extract analytes from samples.
SUMMARY OF THE INVENTION
A device known as the GC sensor is provided for chromatographic analysis.
Conventional GC devices use a traditional tubular analytical column with a
circular cross-section. Instead the GC sensor device has a column which
has a rectangular cross-section. The column is part of a unitary
microstructure which contains the column as well as a sample collection
section and a restrictor. Optionally, a detector can be included in the
unitary microstructure. This unitary microstructure is manufactured using
what are known in the art as LIGA micromachining techniques or other
techniques which will produce high aspect ratio microstructures (HARMs). A
planar section of material which is susceptible to radiation and etching
is irradiated and then etched in solution. The irradiation pattern
produces very tall and very narrow channels in the material. Once a top is
sealed onto the material the four sides of the column are formed.
Rather than serve as the end product, the material subject to etching can
form a mold or model and the ultimate product can be made of metal,
quartz, or some other material. Two or more of the devices can be set in
an array. With each device designed to detect specific compounds, the
array can be tailored for specific application.
A feature of the novel GC device is that it uses less power than a
conventionally configured GC.
An additional feature of the novel GC device is that it can be completely
automated.
An additional feature of the invention is that several of the GC sensors
can be integrated into a sensor array.
An additional feature of the invention is that its small size allows for it
to be carried or worn by an individual.
These and other objects, advantages, and features of this invention will be
apparent from the following descriptions of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the parallel plate embodiment of the
invention.
FIG. 2 is a perspective view of the parallel plate channel structure. The
device is shown without a top plate.
FIG. 3 is a top view of a spiral channel structure. The device is shown
without a top plate.
FIG. 4 depicts a GC sensor in an embodiment which includes a manifold as
top plate and a Peltier cooler as a bottom plate.
FIGS. 5A-5C are plan views of an instrument which includes multiple GC
sensors set in an array.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1, an embodiment of the GC sensor will now be
described. GC sensor 100 will include three general sections indicated by
brackets and identified as sample section 101, restrictor 102, and
analytical column 103. Sample section 101 will include sample section
carrier inlet 104 and sample inlet 105. Although in the embodiment shown
sample inlet 105 and sample section carrier inlet 104 are shown entering
sample section 101 at different points, they could share the same opening.
Restrictor 102 will include restrictor inlet 106 and restrictor carrier
inlet 107.
Analytical column 103 includes first pressure sensor 108, second pressure
sensor 109, detector 110, and make-up gas port 111. Some detectors require
more gas flow than is used in the column. Make up gas port 111 provides
this extra flow when needed. As shown in FIG. 1, sample section 101,
restrictor 102, and analytical column 103 can all be part of a single
layer microstructure sensor 100. The section of analytical column nearest
detector 110 is the detector end; the section nearest restrictor inlet 106
is the intake end.
In one preferred embodiment, the entire parallel plate channel structure
200, shown schematically in FIG. 1, has overall dimensions of 4 cm
wide.times.10 cm. long.times.0.5 cm. high, resulting in a channel which is
2000 microns high, 50 microns wide and 10 meters long. Restrictor 102 and
sample section 101 are fluidly connected to analytical column 103 and have
similar cross-sectional dimensions but are not as long as analytical
column 103.
Preferably the proportionate lengths of analytical column 103, restrictor
102, and sample section 101 are in the range of 70/15/15 to 70/20/10.
These ranges are for an embodiment in which the channel is uniform
throughout GC sensor 100. In other embodiments analytical column 103,
restrictor 102, and sample section 101 can have different cross-sectional
dimensions and the proportionate lengths can be varied.
FIG. 2 depicts one perspective view of a parallel plate channel structure
200 with parallel plate channel 201. This type of parallel plate structure
is used for all three sections of GC sensor 100 depicted in the schematic
view in FIG. 1. Parallel plate channel 201 will include straight channel
portions 202 and curved channel portions 203. Each curved channel portion
203 will have inner radius 204 and outer radius 205. In a preferred
embodiment inner radius 204 and outer radius 205 of each curved channel
will be centered about the same point. This feature of the concentric turn
radii, together with straight channel portions 202 being connected at
alternating ends, will promote laminar flow though parallel plate channels
201.
In another embodiment, sample section 101, restrictor 102, and analytical
column section 103 can be constructed using spiral channel structure 300.
A top view of spiral structure 300 and spiral column 301 is shown in FIG.
3. Because one cannot make lateral connections to inner sections of spiral
column 301 without crossing outer sections of the same spiral column 301,
connections to spiral column 301, such as those for sample inlet 106 and
sample vent 105, are made either though the top (not shown) or bottom of
spiral channel structure 300. Although such top and bottom connections
could also be made for parallel plate channel 201 shown in FIG. 2, such
connections are only required for the inner sections of spiral column 301.
The methods by which the microstructure devices described herein are
manufactured will now be described. Although these methods are discussed
so as to fully enable the invention, it is the intention of the inventor
that the scope of the invention includes other methods of manufacture,
including those discovered in the future, so long as the methods produce
the devices described and claimed herein.
In order to achieve the extremely small dimensions necessary for the GC
sensor, micro-manufacturing techniques must be used. For the accuracy and
size required for gas chromatography, it is believed that the preferred
methods of manufacture for the GC sensor described herein will be the
so-called LIGA method or other HARM manufacturing methods.
As discussed above, in GC the analytes are separated into their various
compounds as they elute from the analytical column. If the analytical
column has a very large cross-section the various compounds will elute
from the column in wide bands. Wide bands are undesirable because there is
a greater chance that the wide band of one compound will overlap with the
wide band of another compound, thereby causing co-elution of each compound
from the analytical column.
Conversely, if the cross-section of the column is made smaller the specific
compounds in the analyte will separate and elute from the analytical
column in very narrow bands. These narrow bands allow for more complete
separations by the column. Therefore it is desirable to achieve
cross-sections as small as possible. These small cross-sections are best
achieved by microstructure manufacturing techniques.
Conventional gas chromatographic capillary columns are typically small open
tubes with internal diameters of 270 to 530 microns and lengths of 10 to
30 meters. The inside walls of these columns are coated with a thin even
layer of organic polymer, the GC liquid phase, to a thickness of typically
less than one micron. As the diameter of the columns is reduced and the
length increased, peak widths become more narrow following predictable
chromatographic theory. This narrowing of peak widths, resulting in higher
resolution between closely eluting compounds, is a beneficial result of
using very narrow column dimensions.
Unfortunately, as the column diameter is decreased, the benefits of
increased resolution are somewhat offset by the need for higher carrier
gas pressures and lower amounts of sample that can be injected before the
column overloads. In the current invention the analytical column will be a
rectangular structure with high aspect ratio dimensions (i.e., very narrow
and tall, or very wide and short) instead of the conventional cylindrical
tube used in past GC technology. Although others have attempted to design
rectangular cross-section columns in the past, the devices have been hard
to reproduce accurately and easily.
The practical challenges in manufacturing rectangular tubing have prevented
widespread development and acceptance of GCs with columns having a
rectangular cross-section. The use of LIGA and other HARM manufacturing
techniques not only allows the fabrication of such columns, it also allows
one to make these columns with very narrow dimensions for extremely high
resolution. Such small size columns possess, to an extreme degree, the
positive attributes discussed above without the over-pressure and overload
characteristics of conventional narrow band tubular columns. HARM
techniques also allow for the manufacture of such devices which are
mechanically rugged and accurately reproducible.
Parallel plate or spiral columns produced using LIGA or HARM techniques
offer a means for realizing the high resolution capabilities of microbore
GC columns without the usual sacrifice in sample capacity and dynamic
range. For example, rectangular parallel plate columns, having
cross-sections equivalent to the internal diameters of narrow bore tubular
columns, can have an order of magnitude more chromatographic surface area,
and thus sample capacity, than conventional capillary columns. The
conventional gas chromatography model predicts a decrease in resolution
with an increase in column diameter. This resolution loss follows from the
assumption of laminar flow in the column.
Under laminar flow conditions, the carrier gas velocity across the column
cross section is described by a parabolic function that varies from a
maximum in the center of the column to zero at the column wall. This means
that analyte molecules distributed homogeneously across the columns cross
section are carried down the column at different velocities depending on
whether they are situated near the center or near the sides of the column.
The result of this flow velocity variation is an increase in the width of
the eluting analyte band.
Because in the present invention the columns are very narrow the flow
velocity variation is decreased. Yet because the columns are also very
tall a larger amount of sample can be analyzed. In the rectangular
cross-section column of the current invention, as an analyte molecule
elutes from the vertical sidewall the molecule moves only away from the
vertical sidewall and towards the detector end of the column. The analyte
molecules exhibit little or no movement in the up and down direction, the
direction parallel to the vertical sidewalls and perpendicular to the top
and bottom walls of the column.
LIGA, a term derived from the German words for the process, involves
irradiation of a photoresist substrate material, such as polymethyl
methacrylate (PMMA). The substrate is chosen so that after being exposed
to radiation, those irradiated portions can be etched away with an
appropriate etching solutions. LIGA techniques are discussed generally in
W. Ehrfeld,et al, "LIGA Process: Sensor Construction Techniques Via X-Ray
Lithography," Technical Digest IEEE Solid State Sensor and Actuator
Workshop, 1988, pp. 1-4.
Selective portions of the substrate will be irradiated in a pattern which
is the desired shape of the structures to be created, or a negative of
those structures. The preferred type of radiation is synchronized x-ray
photons generated by a synchrotron. Synchrotron radiation is preferable
because its strength and frequency can be accurately regulated to control
the depth to which the substrate is to be etched.
Several materials could be used for the GC sensor. One could use the LIGA
techniques to etch a substrate layer which would serve as a negative for
the ultimate shape of the GC sensor. This substrate could then be
electroplated with a metal, such as nickel, to create GC sensor 100. The
surfaces of the interior channels, such as parallel plate channel 201 or
spiral channel 301, are deactivated using electropolishing or surface
bonding techniques. The metal structure can also be used a model for the
creation of plastic or ceramic molds, and these molds could be used to
create additional metal GC sensors. If the electroplating process is
employed to create metal structures the substrate layer must include below
it a metal plate onto which the metals may be electroplated.
In another embodiment, one could use LIGA techniques to etch a substrate
which is as a positive of the GC sensor. This substrate would then be
electroplated with a metal and the resulting metal structure would be a
negative. This metal negative could be used as a mold to create final
structures. This could be accomplished by filling the metal negative with
plastic or ceramic. In a particularly preferred embodiment, the GC sensor
would be constructed of quartz or a rigid solgel silica material.
Preferably, these non-metallic GC sensors will be coated with a thin metal
layer so that they are better conductors of heat.
A process for the manufacture for parallel plate channel structure 200 will
now be described. The process will discuss an embodiment of parallel plate
channel structure 200 which is composed of quartz coated with metal. The
process begins with an initial substrate of material susceptible to X-rays
and etching (e.g. PMMA or other photoresist material). Selective portions
of the PMMA are exposed to x-ray photon radiation, leaving a substrate
which has the general appearance of parallel plate channel structure 200.
The selective irradiation of the PMMA is performed by beam direction
techniques or by placing a patterned mask over the PMMA. The strength and
wavelength of the x-ray photons will be controlled so that the radiation,
and subsequent etching, will remove almost all of the PMMA in parallel
plate channels 201 but will not remove bottom layer 206. The top surface
of bottom layer 206 serves as channel bottom surface 207 of parallel plate
channel 201.
In an alternative embodiment one could also begin with a dual layer
material. Bottom layer 206 could be made of metal and the remainder of the
substrate would be constructed of a material susceptible to radiation and
etching (e.g. PMMA) which was bonded to the metal. The dual layer material
could then be irradiated and etched to create a structure with the
appearance of parallel plate channel structure 200. Additional metal may
then be electroplated onto this exposed metal surface, filling parallel
plate channel 201 up to a desired thickness.
The structure is exposed to radiation and etched again, and only the metal
bottom layer 206 and the electroplated metal structures remain. The
resulting metal structure is a negative of parallel plate channel
structure 200. This negative is filled with quartz to create a parallel
plate channel structure 200 made of quartz. Parallel plate channel 201 is
then coated with a thin metal layer.
For all of the methods and materials discussed above the resulting
structure will have the general appearance of parallel plate channel
structure 200. Parallel plate channel structure 200 will be sealed on the
top with a top plate (not shown). For a single GC sensor 100 the top plate
will be constructed of a material which can be bonded to, and which is the
same as or compatible with, the material in parallel plate structure 200.
The top plate could be a simple plate, a manifold with ports and openings
which make up the various connections to GC sensor 100 shown in FIG. 1, a
temperature control means, or the bottom plate of another GC sensor 100 if
the sensors are stacked in an array.
FIG. 4 shows complete GC sensor 400 which includes top plate 402 and
channel structure 401. In the embodiment of FIG. 4 GC sensor 400 will also
include temperature control means 403. In one particularly preferred
embodiment temperature control means 403 is a device is known in the art
as a Peltier cooler, which can be used for the temperature programming
techniques which will be employed with GC sensor 400. One could also
employ an electrically resistive plate as temperature control means 403.
In one preferred embodiment channel structure 401 will be made of nickel,
which conducts heat very effectively. In this embodiment electrically
resistive heating of GC sensor 400 itself can be used, eliminating the
need for temperature control means 403. Because nickel has excellent
thermal conduction properties, temperatures will be homogenous across
relatively thin (0.4 mm) sections of nickel which make up channel
structure 401. Those skilled in the art may use other metals and other
materials which are inert to the GC process and which can be heated
homogeneously. The miniaturization of the chromatograph and the heating of
only those components which must be heated allows for efficient power
usage not possible with conventional GCs.
In another embodiment top plate 402 is an electrically resistive plate used
in combination with a Peltier cooler as temperature control means 403.
Each such device can be connected to a temperature programming
microprocessor (not shown) via electrical leads 404. Such a combination
will provide for the use of precise temperature programming techniques
with GC sensor 400.
In another preferred embodiment, more than one electrical circuit can be
made on a parallel plate structure 200 or on an adjacent plate. In this
embodiment discreet portions of GC sensor 100 can be heated to one
temperature while others are left at ambient temperature or heated to a
different temperature.
In the embodiment depicted in FIG. 4 top plate 402 is a manifold bonded
onto channel structure 401. The manifold includes the ports, valves, and
connections shown in a schematic view in FIG. 1. Manifold 402 includes
detector port 405, sample section carrier inlet 104, sample inlet 105,
restrictor inlet 106, restrictor carrier inlet 107, first pressure sensor
108, and second pressure sensor 109.
FIGS. 5A through 5B depict sensor array 500 which will include one or more
GC sensors 501. GC sensors 501 can include the elements shown in FIG. 4;
however for purposes of illustration in GC sensors 501 in FIG. 5A through
5B are shown in plan view only. Sensor array 500 will include array
housing 502. In a preferred embodiment each GC sensor 501 can be designed
to check for specific compounds. This ability to speciate each GC sensor
100 may be achieved by variances in column dimensions, column coating,
temperature programming, type of detector, and other design choices.
Although the embodiment of sensor array 500 depicted in FIGS. 5A-5B has
three GC sensors 501, one skilled in the art can design sensor array 500
so as to include any number of GC sensors. Additionally, because each GC
sensor 501 is modular, specific GC sensors can be interchanged on sensor
array 500 for particular applications.
The inventor believes the essence of the invention is the use of the LIGA
or HARM techniques, which allow for the creation of high aspect
microstructures not achievable with other manufacturing techniques, to
produce a gas chromatograph which is extremely small, yet accurately and
reliably reproducible; the devices produced from such a method; and the
uses of that device.
With reference to FIG. 1 the operation of GC sensor 100 will now be
described. Column 103 will be coated with bonded and cross-linked GC
liquid phase. Sample section 101 and restrictor 102 can be uncoated.
Carrier gas flow is maintained through the column by applying the
appropriate carrier gas pressure at sample section carrier inlet 104. The
sample to be tested is drawn into the sample loop while the instrument is
at ambient temperature.
The sample may be flowed into sample section 101 by flowing sample gas (not
shown) into sample section inlet 105 at a higher pressure that the
pressure at restrictor inlet 106. Preferably, this pressure differential
is created by placing a vacuum at restrictor inlet 106. These settings
will cause the sample to be drawn into sample section inlet 105, which
includes a check valve. This method of sample intake is not the only
method available; the sample could be drawn or pumped into sample section
101 in many ways using different pressure differentials at the various
ports of sample section 101.
As the sample is flowed into sample section 101, semivolatile analytes are
trapped on the portion of sample section 101 nearest sample inlet 105
while volatile analytes fill the remaining void space of sample section
101. Alternatively, one can place a vacuum at sample section inlet 105 and
draw the sample gas in through restrictor inlet 106, in which case the
semivolatile analytes are trapped on the portion of sample section 101
nearest restrictor inlet 106.
In order to inject the analytes into column 103, restrictor carrier inlet
107 is closed and carrier gas is flowed into sample section carrier inlet
104. The amount of analytes injected will be determined by the length of
time restrictor carrier inlet 107 is closed and sample section carrier
inlet 104 is open as well as the pressure differential between restrictor
carrier inlet 107 and sample section carrier inlet 104. This time can be
on the order of 100 milliseconds and the pressure differential may be 15
to 25 psig.
After the desired quantity of analytes have been injected into column 103,
restrictor carrier inlet 107 is re-opened and the temperature in column
103 is ramped from initial to final temperature at rates of 1 to 20
degrees C. per second. If semivolatile analytes are being analyzed, sample
section carrier inlet 104 is reopened during temperature programming but
after the volatile components have been injected or cleansed from the
loop. As the temperature of GC sensor 100 is raised, semivolatile analytes
move from sample section 101, through uncoated restrictor 102, and onto
coated column 103 for separation during temperature programming. Eluting
compounds are detected with detector 110. It will be obvious to those
skilled in the art to use flame or photo-ionization detection, thermal
conductivity detection, or any of several known methods to perform the
detection function on the eluting analytes as they exit column 103.
There are of course other alternate embodiments which are obvious from the
foregoing descriptions of the invention, which are intended to be included
within the scope of the invention, as defined by the following claims.
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